The ultimate objective of this program is cure of children with leukemia. The program is a coordinated effort of therapy and study which includes therapeutic trials aimed at prolonging leukemia-free survival with the more efficient use of conventional agents and the development of new agents, studies of the biology and pathogenesis of leukemia and studies of the effects of leukemia and its therapy on normal tissues. The program consists of seven interrelated projects: (1) Primary therapy of acute lymphocytic leukemia. (2) Primary therapy of acute non-lymphocytic leukemia. (3) Therapy of relapse of leukemia. (4) Leukemia cell kinetics. (5) Studies of in vitro growth of normal and leukemia marrow. (6) Pathogenesis and therapy of pneumonia. (7) Pathogenesis of pancytopenia in mice. All projects have the same ultimate objective and, though a wide variety of disciplines is involved, the organization structure provides the means for a unified, coordinated effort.